People affected by rare diseases often have limited coping resources and sometimes face stigma. They build communities with others who share their conditions, but not all members may benefit from these communities. This study investigated how adults with a rare genetic health condition (Alpha-1 antitrypsin deficiency; AATD) think about both the Alpha-1 community and public stigma about AATD, and how these cognitions were associated with their communication responses and well-being. The results showed that people with AATD encountered stigmatization from various sources, including family, employers, healthcare providers, and insurance companies. Stronger public stigma predicted more secrecy, more stress, and less available support. Stronger group identification with the Alpha-1 community predicted less secrecy; stronger group activism predicted more available support and more communication to challenge stigmatizers. Post-hoc analyses showed significant interactions between public stigma and group cognitions on communication to challenge stigmatizers. Practical implications for bolstering communities to improve the well-being of people with rare diseases were discussed.